1. Field of the Invention
The present invention relates to a positive photoresist composition and a multilayer resist material using same. In particular, it relates to a positive photoresist composition which provides, in the formation of isolated patterns rather than dense patterns of lines and spaces (L&S), a resist pattern having a high film residual rate, excellent development contrast, satisfactory definition (image resolution), exposure margin, focal depth range properties and sectional shape. In addition, it relates to a multilayer resist material using the positive photoresist composition.
2. Description of the Related Art
Hitherto, photoresist compositions comprising an alkali-soluble resin and a quinonediazide group-containing compound have been extensively put to a practical use in the production of semiconductor devices and liquid-crystal devices, since they are excellent in definition, sensitivity and etching resistance.
In the current manufacture of ultralarge-scale integrated circuits (Ultra LSI), a high definition of less than half a micron, for example, of 0.4 .mu.m, 0.35 .mu.m or the like is required. In addition, there are demands for photoresist compositions which can form a resist pattern being excellent definition, exposure margin and focal depth range properties with a good rectangular sectional shape.
It is, however, difficult to form a rectangular resist pattern having an excellent sectional shape in the formation of fine patterns of 0.4 .mu.m or less. As a pattern becomes finer, the rate of change of the pattern shape increases due to shift of focus (i.e., deterioration in focal depth range properties). Particularly, the overall pattern tends to be narrower to the minus side (where the focus shifts or deviates from the surface of a resist film upward). This phenomenon may, at the worst, invite the twisting of the pattern formation. This phenomenon occurs more markedly in the formation of an isolated pattern than that of a dense pattern. As described above, conventional photoresist compositions are problematic in that the margin of focus shift (defocus) in which an excellent pattern profile can be produced is narrow, and as a result, slight shifts of focus in a practical exposure operation leads to scattering of the pattern profiles.
As a means of preventing deformation of a pattern shape due to light reflection from a substrate having high reflectivity such as a silicon substrate, an aluminium film, a tungsten silicide film, a measure in which an anti-reflection coating is formed between a substrate and a photoresist film (bottom anti-reflection coating (BARC) method) has been proposed. However, with such a method, the photoresist coating formed on an anti-reflection coating is disadvantageous in that the overall pattern tends to become even narrower due to a shift in focus to the minus side.
Furthermore, a phenomenon in which an isolated pattern becomes narrow overall at the minus side of the focus is thought to be attributable to the fact that such an isolated pattern is more easily subject to light reflection from the substrate than a dense pattern shape is.
Accordingly, a positive photoresist composition which has improved pattern shape in defocus to the minus side and excellent focal depth range properties is desired.
Additionally, a shift of focus to the plus side is also undesirable. Such a shift or defocus to the plus side disadvantageously invites film reduction. As a measure of improving the focal depth range properties at the plus side, the present inventors found that addition of a sulfonyl halide having a specific structure to a photoresist composition effectively inhibits tailing in the bottom and in the pattern top, and reported this in Japanese Patent Application No. 8-305873. According to this technique, focal depth range properties at the plus side can be remarkably improved not only on a substrate without an anti-reflection coating but also on an anti-reflection coating, which results in production of a photoresist coating which exhibits a small rate of change in the pattern shape, that is, has excellent focal depth range properties.
This technique, however, leads to a phenomena in which the pattern top becomes larger and the bottom becomes narrower when a defocus occurs to the minus side. In other words, the pattern has a sectional shape like a reverse-pyramid or reverse-trapezoid, which tends to lead to twisting of the pattern formation. This tendency increases in the formation of an isolated pattern as compared with that of a dense pattern, and increases with a fine pattern or a defocus shifting to the minus side.
It is also thought that since the distance between a light source and a substrate at the plus side of a focal point is shorter than a predetermined one, overexposure occurs, and hence the pattern shows a film reduction tendency at this side.
Accordingly, it is an object of the present invention to provide a positive photoresist composition which exhibits a high film residual rate, an excellent development contrast between exposed portions and unexposed portions, satisfactory definition, exposure margin and sectional profile or shape, and which provides a resist pattern having a satisfactory shape, particularly when the focus shifts to the minus side, and shows superior focal depth range properties, and a multilayer resist material using the aforementioned positive photoresist composition.
It is another object of the present invention to provide a positive photoresist composition with such excellent focal depth range properties that a resist pattern having an excellent shape can be formed even in the defocus at the minus side and the plus side.